Science Daily – In a new (circa 2004) study, NASA
and United States Geological Survey (USGS)
scientists found that retreating glaciers in
southern Alaska may be opening the way for future
earthquakes.

The study examined the likelihood of increased
earthquake activity in southern Alaska as a
result of rapidly melting glaciers. As glaciers
melt they lighten the load on the Earth’s crust.
Tectonic plates, that are mobile pieces of the
Earth’s crust, can then move more freely. The
study appears in the July issue of the Journal of
Global and Planetary Change.

Jeanne Sauber of NASA’s Goddard Space Flight
Center, Greenbelt, Md., and Bruce Molnia, a
research geologist at USGS, Reston, Va., used
NASA satellite and global positioning system
receivers, as well as computer models, to study
movements of Earth’s plates and shrinking
glaciers in the area.

“Historically, when big ice masses started to
retreat, the number of earthquakes increased,”
Sauber said. “More than 10,000 years ago, at the
end of the great ice age, big earthquakes
occurred in Scandinavia as the large glaciers
began to melt. In Canada, many more moderate
earthquakes occurred as ice sheets melted there,”
she added.

Southern Alaskan glaciers are very sensitive to
climate change, Sauber added. Many glaciers have
shrunk or disappeared over the last 100 years.
The trend, which appears to be accelerating,
seems to be caused by higher temperatures and
changes in precipitation.

In southern Alaska, a tectonic plate under the
Pacific Ocean is pushing into the coast, which
creates very steep mountains. The high mountains
and heavy precipitation are critical for glacier
formation. The colliding plates create a great
deal of pressure that builds up, and eventually
is relieved by earthquakes.

The weight of a large glacier on top of these
active earthquake areas can help keep things
stable. But, as the glaciers melt and their load
on the plate lessens, there is a greater
likelihood of an earthquake happening to relieve
the large strain underneath.

Even though shrinking glaciers make it easier for
earthquakes to occur, the forcing together of
tectonic plates is the main reason behind major
earthquakes.

The researchers believe that a 1979 earthquake in
southern Alaska, called the St. Elias earthquake,
was promoted by wasting glaciers in the area. The
earthquake had a magnitude of 7.2 on the Richter
scale.

Along the fault zone, in the region of the St.
Elias earthquake, pressure from the Pacific plate
sliding under the continental plate had built up
since 1899 when previous earthquakes occurred.
Between 1899 and 1979, many glaciers near the
fault zone thinned by hundreds of meters and some
completely disappeared. Photographs of these
glaciers, many taken by Molnia during the last 30
years, were used to identify details within areas
of greatest ice loss.

Field measurements were also used to determine
how much the glacier’s ice thickness changed
since the late 19th century. The researchers
estimated the volume of ice that melted and then
calculated how much instability the loss of ice
may have caused. They found the loss of ice would
have been enough to stimulate the 1979 earthquake.

Along with global positioning system measurements
made by Sauber and Molnia a number of NASA
satellites were used to document glacier
variability. Data from Landsat-7 and the Shuttle
Radar Topography Mission (SRTM) were used to
study glacier extent and topography. Currently,
NASA’s ICESat satellite is being used to measure
how the glacier thicknesses are changing.

“In the future, in areas like Alaska where
earthquakes occur and glaciers are changing,
their relationship must be considered to better
assess earthquake hazard, and our satellite
assets are allowing us to do this by tracking the
changes in extent and volume of the ice, and
movement of the Earth,” Sauber said.

Note: This story has been adapted from a news
release issued by NASA/Goddard Space Flight
Center.

>
>
> *Lowest Streamflow in 110 Years Recorded in North Carolina*
>
> *RALEIGH, North Carolina*, August 31, 2007 (ENS) – The lowest average
> August streamflow in 110 years of North Carolina recordkeeping was
> measured last month on the Tar River at Tarboro, in the east-central
> part of the state.
>
> Streamflow figures released by the U.S. Geological Survey, USGS, on
> Friday show that the hot, dry days of August brought record lows to many
> of the state’s rivers and streams amidst worsening drought conditions.
> People across most of eastern North Carolina are being asked to conserve
> as much water as they can.
>
> The USGS and its federal, state, and local cooperators maintain 270
> streamgaging stations and 39 monitoring wells throughout North Carolina.
>
> These measurements show that the lowest average August streamflow on
> record occurred at 12 other monitoring stations in the state, but not
> compared to a 110 year period as on the Tar River.
>
> All of these other 12 sites have at least 35 years of record, and most
> of the sites have more than 50 years of record. Nine of those sites are
> located in central North Carolina, with the others on the coastal plain
> or in the mountains.
>
> August 2007 streamflows at 17 eastern North Carolina monitoring stations
> are lower than those measured during the 1998 – 2002 drought, when
> minimum streamflow records were established throughout much of the state.
>
> Records for the lowest daily streamflow ever measured were established
> at three monitoring stations.
>
> On August 17, streamflow at the Oconaluftee River, which runs through
> Swain County in western North Carolina, was 72 cubic feet per second,
> compared with the previous record low of 110 cubic feet per second
> established during the 1987 – 1988 drought.
>
> During more than half of August, streamflows at this site were lower
> than the previous record minimum.
>
> Record daily minimum streamflows also were established at Buckhorn Creek
> in Chatham County, southwest of Raleigh.
>
> On Fishing Creek in Edgecombe County streamflow has been measured
> continuously since 1923, and the minimum daily streamflow measured there
> in August 2007 was about 2.5 times lower than the previous minimum.
>
> Effects of the drought on groundwater levels are variable across the
> state, the USGS reports. Groundwater levels in unpumped wells in western
> North Carolina and in the outer coastal plain are approaching the levels
> observed during the 1998 – 2002 drought.
>
> Groundwater levels at most locations throughout central North Carolina
> however, are only slightly below average for August, despite the fact
> that streamflows at many locations are at record low levels for August.
>
> The heat and low streamflows also are affecting stream water
> temperatures, which can adversely affect fish and biological communities.
>
> Monthly average water temperatures at 16 monitoring stations across the
> state averaged about three degrees Fahrenheit greater than normal for
> the month.
>
> At Hyco River in Person County, where water temperature has been
> measured since 1985, streamflow temperatures in August were about four
> degrees greater than average.
>
> Water temperatures in the sounds and estuaries also are affected. In the
> Neuse River at New Bern, water temperature was about 3.5 degrees higher
> than normal for August.
>
> The U.S. Drought Monitoring system has classified 12 counties in the
> southwestern tip of the state to be undergoing the highest level of
> drought, called Exceptional Drought. They are Buncombe, Cherokee, Clay,
> Graham, Haywood, Henderson, Jackson, Macon, Madison, Polk, Swain, and
> Transylvania counties.
>
> The North Carolina Drought Management Advisory Council is urging all
> water users in this area to limit water usage to those uses that are
> essential to ensure public health and safety and to prepare for the
> likelihood of community water systems requiring water rationing.
>
> Maps and graphs are on the USGS North Carolina Drought Watch
> < http://nc.water.usgs.gov/drought/> site.
>
> Follow the North Carolina Department of Environment and Natural
> Resources Summary of Water Conservation Level Status by location at:
> http://www.ncwater.org/Drought_Monitoring/reporting/displaystate.php
>
> Copyright Environment News Service (ENS) 2007. All rights reserved.
>
>
>
>
> < http://www.ens-newswire.com/ens/aug2007/2007-08-31-091.asp#>